Catheters using an extensible balloon have many areas of use in medical technologies. It is often related to the treatment of restrictions in certain organs which are accessible only via narrow passages. With the balloon in a deflated state it is introduced into the site of treatment and is then made subject to expansion. For certain purposes balloons having a limited elasticity in a radial direction are used i.e. the balloon takes a predetermined shape when distended, for example cylindrical shape.
Such balloon catheters have been extensively used to open restrictions, so called stenoses, in for example the vascular system. This treatment, so called PTC- or PTCA-techniques, take place under several bars of pressure, and it is therefore important that the balloon can expand only up to the predetermined diameter so as to avoid damage to the vessel by over-dilation.
For the treatment of benign prostate enlargements (BPH) it has been suggested to dilate urethra and prostate using a balloon of restricted radial expansion which, when distended from a dilated diameter of about 5 to 7 mm forms a cylinder having a diameter of about 30 mm. The inflation of the balloon must take place under high pressure in view of the resistance of the surrounding tissue.
As a material for dilation balloons for PTA, PTCA or dilation of the prostate different flexible but inelastic materials are used. One example is polyethylene terephtale (PET). This material can be pre-shaped and has high mechanical strength in spite of a wall thickness of only 0.03 to 0.04 mm which is an advantage, in particular in relation to dilation of fine blood vessels.
A drawback of such inelastic material is, however, that folds are formed when the balloon is in an unexpanded state, for example when the balloon catheter is introduced into or withdrawn from fine bodily ducts. In U.S. Pat. No. 5,423,755 (Kesten et al.) there is described a balloon catheter for dilation of urethra and prostate, the balloon being made of such inelastic material. In order to reduce the formation of folds both ends of the dilation balloon are each attached to two telescopically arranged central tubes. A spring has bias separate the two tubes axially so that the balloon is maintained in a stretched position when the system is unpressurised. When pressure is supplied the balloon diameter increases at the same time as the balloon length will be reduced in view of the acting forces until the predetermined balloon dimension in regard to diameter and length has been reached. In this manner the formation of folds across the balloon will be reduced but the problem of axial folding remains.
In the patent No GB 1566 674 (Hanecka et al.) there is described a similar balloon catheter for dilation of blood vessels, oesophagus, ductus scholedochus, the formation of folds being reduced by the use of two co-axial tubes, one slidable, within the other to prevent an irregular and unlimited extension. The balloon is reinforced by a synthetic fabric embedded in the balloon. The filaments of the fabric extend along helices of opposite sense so that only a limited extension in the radial direction is allowed. For introduction the balloon is stretched in an axial direction increasing its length by 60% and simultaneously decreasing the diameter to 40% of the pressurised balloon. At pressurising the balloon will expand in a radial direction to the desired diameter while its length becomes shortened. In case of stenoses which are longer than the balloon the catheter is inserted further and the expansion repeated.
In U.S. Pat. No. 5,314,443 (Rudnick) there is described a similar balloon catheter with two co-axial slidable tubes where the elastic balloon material is constituted by for example polyurethane, silicone or latex reinforced with glass fibre, nylon or carbon fibres, which are materials of low elasticity.
In U.S. Pat. No. 4,637,396 (Cook) there is described a balloon catheter using an elastic balloon for dilation to a certain predetermined diameter. The balloon wall consists of three layers, one inner elastic tight urethane membrane, a middle layer of a knitted fabric tube and an outer layer of an elastic impervious urethane membrane. The three materials are attached together at their ends and form a tube-shaped balloon.
The material of the knitted fabric tube is a yarn of limited elasticity, for example composed of inelastic strong fibres, such as Dacron, and by elastic fibres, for, example Spandex. When such yarn is stretched it is extended by its elasticity up to a certain limit at which the inelastic fibres of the material are fully stretched and can absorb relatively strong forces.
The advantage of this balloon catheter is that there is a minimum of fold formation and that there is no change of length when the balloon is inflated or when the pressure is released. Accordingly, this results in a simple design with the balloon attached to one single central tube. In this manner a balloon is obtained which has the same fixed length both as deflated and inflated.
When treating certain human organs it is important that the dilatation takes place only at a precise predetermined site and for a length which is adapted to the restriction to be treated. As an example there can be mentioned dilatation of an enlarged prostate at BPH. In dilatation using for example ASI UROPLASTI™ Dilatation system, Advanced surgical intervention Inc. USA, it is important that the proximal end of the balloon is positioned at the apex adjacent to the external sphincter and that it should not extend beyond the bladder neck. Since the length of the prostate varies to a large extent from patient to patient this length must first be determined using a special calibration catheter with a Foley balloon in the distal end under cystoscopy after which the urologist selects the correct balloon size. Therefore, nine catheters with balloon lengths in a range between 15 to 55 mm must be available with 5 mm increments. To allow exact positioning of the selected balloon catheter this has a separately expandable Folley balloon at the distal end of the catheter for precise placement of the distal end of the dilatation balloon at the bladder neck.
In certain cases restrictions are treated with a combination of pressures and heat from a heat-releasing balloon. U.S. Pat. No. 5,257,977 (Eshel) thus describes a method for the treatment of enlarged prostate with an expandable balloon. A heater fluid supply inflates under a pressure of 1–4 atm a balloon and provides a pressure and heat treatment to the prostate and bladder neck. The corresponding catheters commercially available from Argomed Inc, Morrisville, USA. Even in this case catheters in 9 different balloon lengths from 2 to 6 cm are available. This is, of course, a significant disadvantage and involves high costs for manufacture and storage both for producer and hospital.